This invention relates generally to an ink level indicator and an ink cartridge having the same and, more particularly, to ink level indicator for use in a vented foam-filled ink jet print cartridge having a window for residual ink level indication.
The problem of monitoring the ink volume or ink level in all types of ink-jet printers with ink reservoirs has been variously addressed. So-called backpressure indicators require a plurality of complex seals within the ink cartridge assembly and are therefore relatively expensive and tend to be unreliable. Other ink volume indicators rely on a system that measures the ink bulk electrical conductivity. The electrical conductivity of ink is difficult to control and there is likelihood that future ink improvements could make such a system obsolete.
There have also been attempts in systems to count the “dots” or ink drops dispensed from an ink jet print cartridge. The counters, actuators and sensors needed for such systems may cause the systems to be relatively expensive to build. Furthermore, accuracy may be compromised by the need to assume an average drop volume for all print cartridges. Interruptions such as caused by removal of a print cartridge from a printer or shut-down of the printer are a possible further source of unreliability since the record of the number of drops dispensed from the ink jet print cartridge since the last update is likely to be lost.